1. Field of the Invention
Present invention relates to nozzle plate for ink jet printer head and particularly relates to a method of manufacturing nozzle plate for ink jet printer head using the silicon process and a nozzle plate manufactured thereby.
2. Description of the Prior Art
In ink jet printer head, ink contained in ink supply unit is supplied to the writing unit through ink supply pipe and the writing unit executes printing by jetting ink provided from ink supply unit into material where to be written. Whence ink is sprayed through nozzle formed at nozzle plate onto material where to be written.
It is important to make the jetted inkdrop sizes to be fine and uniform in order to improve printing characteristics; for which purpose of fine and uniform size, the nozzle outlet part diameter must be formed fine and uniform.
By the way, meniscus exposed to atmosphere at nozzle outlet part arouses vibration owing to inertial flow of ink to refill the jetted ink quantity after ink jetting during which meniscus vibration the ink cannot be jetted out. Therefore it is important to quickly attenuate meniscus vibration and stabilize it in order to reduce interval unto next ink jet. Printer head jet frequency could be enhanced if meniscus vibration could be quickly reduced.
Method of reinforcing the attenuation function by reducing the nozzle outlet part diameter formed at nozzle plate is used as a means for quickly attenuating the meniscus vibration.
Thus in ink jet printer head, the nozzle outlet part formed at nozzle plate is important factor influencing the inkdrop jet performance, the stability after ink jetting and the printing characteristics.
Conventionally it was made that nozzle plate outlet part cross-section shape has straight pipe portion of suitable length to reduce nozzle plate outlet part diameter.
Nozzle plate having suitable length of straight pipe portion at nozzle outlet part can quickly attenuate meniscus vibration because the portion diameter is relatively smaller than at other portions.
As for nozzle plate having suitable length of straight pipe portion at outlet part, straight line movability of ink is improved because ink flowing through nozzle plate outlet forms a laminar flow at the straight pipe equivalent portion when ink is jetted from where printer head has been constructed by assembling channel, chamber, actuator etc. above the said nozzle plate. Therefore precision or dispersion at position where inkdrop lands on the material on which to be written will be improved so that print status will be improved.
Usually metal has been used for nozzle plate material and the method of electroforming and the method of micropunching and polishing process have been used to make the nozzle plate using a metal.
In method of electroforming process, photoresist is thin coated on substrate and then it is patterned. Electroplating material grows when electric current flows after substrate where pattern has been formed is immersed in electrolyte after which the electroplating is stopped if electroplating material has grown to size of nozzle to be used. Nozzle plate where nozzle has been formed is completed by removing (photoresist that is formed on) substrate after finishing the electroplating.
Method of forming the nozzle plate by electroforming process has advantage that the manufacturing process is simple and mass production is feasible. But there are problems that it is difficult to form a straight pipe portion at outlet part of nozzle because cross sectional shape of formed nozzle has natural arc type and that bond stability is decreassed because nozzle plate area is decreased which is bonded at printer head when nozzle plate is to be bonded at printer head.
In method of making the nozzle plate by micropunching and polishing processes, metal sheet to be used as nozzle plate is drawn by micropunching pin so that nozzle cross section face is formed beyond depth of opposite surface of the metal sheet. Protruded part of metal sheet after drawing process is removed by polishing process and burr generated on metal sheet by polishing process is removed by electrolytic polishing or chemical polishing.
This method has advantage that cross sectional shape of nozzle may be made at will according to punching pin used and that it is easy to make straight pipe portion at nozzle outlet part. Also it has advantage that when nozzle plate is bonded at printer head the bonding area will be wide so that it will have high stability.
But it has problems that its work processes are complicated as it must go through polishing process to remove protruded part after micropunching, burr generated by this polishing process must be removed by successive polishing processes such as electrolytic polishing or chemical polishing, etc. so that also it needs large scalefacility. And it has problem that production cost rises because there are much micropunching pin damages according to punching duration so that its durable life is short.
In case when nozzle plate is fabricated using metal as above, water repellency treatment should be done on nozzle plate surface and nozzle contacting the ink.
Next in method of fabricating nozzle plate using a laser, polymer such as polyimide is used for nozzle plate material. Nozzle is fabricated in fine pattern by irradiating laser for short time using hot laser on nozzle plate made of polymer.
This method has advantage that polymer itself has water repellency effect so that separate water repellency treatment is not needed but it has problems that yield percentage is low and it is expensive for mechanism when laser is irradiated onto large area. Nozzle plate may be fabricated using monocrystalline silicon instead of metal for a continuous type ink jet head and an ink jet head applying thermal expansion of film or bubble jet.
Anisotropic etching process of silicon among bulk micromachining technique is used if nozzle plate is fabricated using monocrystalline silicon stuff.
Nozzle is fabricated by forming pyramid type hole in silicon substrate of (100) crystal direction using anisotropic etching liquid after shielding other parts than that to be etched, by silicon oxide film or silicon nitride film. Whence shapes of nozzle edge and nozzle cavity are controlled by etching liquid used in etching, etching time and etching rate of silicon.
Nozzle fabricated by this method has problems that straightness is degraded at ink jet and, in case when nozzle is fabricated by isotropic etching after anisotropic etching, degree of etching of each part becomes different from according as etching is repeated so that fabricated nozzles are not uniform.
Purposes of present invention to solve the above problems are to provide fabrication method of nozzle plate where crater and nozzle having straight pipe part using silicon process and silicon wafer stuff and to provide nozzle plate fabricated thereby.
Present invention to achieve the above purposes relates nozzle plate fabrication method comprising a step to provide silicon wafer; a step to form straight pipe part layer under the silicon wafer by doping impurity component, electroplating a metal or forming a polysilicon layer; a step to form crater layer under the straight pipe part layer by electroplating a metal; a step to form nozzle slope part by an isotropic etching after patterning the silicon wafer; a step to form straight pipe part of nozzle outlet part at the straight pipe part layer by dry etching of the straight pipe part layer; and a step to form crater at the crater layer by etching after patterning the crater layer.
And the invention relates nozzle plate fabrication method comprising a step to provide silicon wafer; a step to form straight pipe part layer under the silicon wafer by doping impurity component, electroplating a metal or forming a polysilicon layer; a step to form nozzle slope part by anisotropic etching after patterning the silicon wafer; a step to form straight pipe part of nozzle outlet part at the straight pipe part layer by dry etching of the straight pipe part layer; a step to form photoresist layer under the straight pipe part layer; a step to leave photoresist only at crater part by patterning the photoresist layer; a step to form crater layer by electroplating a metal under the straight pipe part layer; and a step to form crater by removing photoresist.
And the invention relates nozzle plate comprising silicon wafer; straight pipe part layer made of polysilicon, metal or a doping layer formed under the silicon wafer; crater layer formed under the straight pipe part layer by electroplating a metal; nozzle slope part formed at the silicon wafer by anisotropic etching; straight pipe part of nozzle outlet part formed at the straight pipe part layer by dry etching of the straight pipe part layer; and crater formed at the crater layer by etching the crater layer.